Stabilized cationically-curable compositions

Abstract: The present invention provides an energy polymerizable composition comprising at least one epoxy monomer or at least one vinyl ether monomer and an initiation system therefor, the initiation system comprising at least one organometallic complex salt and at least one stabilizing additive. The cured composition provides useful articles or coated articles.

Description: This invention relates to energy-polymerizable compositions comprising a cationically curable monomer and, a two-component initiator, at least one organometallic complex salt, at least one stabilizing additive, and abrasive particles, and a method for curing the compositions. This invention also relates to preparing articles comprising the cured compositions. Epoxides, i.e., organic compounds having one or more terminal or pendant oxirane (epoxy) groups, have been widely used for many years in adhesive compositions. These compounds are commonly cured, or caused to harden, by the addition of a curing or hardening agent. Many epoxy compositions use curing agents that begin to act immediately, or after a short period of time, even at room temperature or lower. These two-part compositions require that the epoxide and the curing agent be stored separately and only mixed immediately before use. A one-part composition has inherent shelf-life stability problems. In many applications, it is desirable for a mixed two-part composition to be stable for a period of days, weeks, or months so that large batches can be prepared to be used as needed. Various attempts have been made to prolong "pot life" prior to cure of curable epoxy compositions. This allows the epoxide and curing agent to be mixed and stored before use as a one-part that is curable upon heating. Generally, it has been found that any increase in pot-life of epoxy compositions results in a corresponding sacrifice of cure speed. Additionally, achieving complete reaction, i.e., where all the epoxide functional groups are consumed, may require longer cure times and/or higher cure temperatures. Various publications disclosing the preparation and/or use of curing agents for epoxy resins and/or other curable compositions are discussed below. European Patent Application 0 511 405A1 teaches the use of onium salts having a nucleophilic pair anion, such as halogenide, perchlorate, alkylsulfate, arylsulfonate, as stabilizers for the polymerization of cationically polymerizable organic compositions, catalyzed by (n 6 -arene) (n 5 -cyclopentadienyl) iron(+1) salt cationic photoinitiators. The pair anion of the onium salt attacks a growing terminal of the polymerization reaction during the curing of the composition leading to rapid termination. U.S. Patent Nos. 5,130,406 and 5,179,179 disclose cationic initiators containing oxygenated sigma-donor ligands. Such initiators suffer from their high hygroscopicity (moisture sensitivity); additionally, these initiators provide very little work time because they must be mixed with the epoxide at low temperatures. Iron-arene salt cationic photoinitiators have been shown to effect the polymerization of pyrrole in the presence of oxygen. (Rabek, et al. Polymer 1992, 33 , 4838-4844.) This polymerization proceeds through proton and hydrogen atom abstraction catalyzed by Fe(III). The polymerization was completely inhibited in the presence of 1,10-phenanthroline. U.S. Patent No. 4,920,182 discloses the use of a photoactivated bis-arene Fe complex that initiates copolymerization of epoxy- and carboxyl-terminated polyesters after exposure to light and subsequent heating. There is, however, no indication of the degree of either pot-life before, or latency, after, photoactivation as well as the speed of cure and its relation to pot-life and latency. U.S. Pat. No. 4,846,905 describes the use of an acid/amine complex as a catalyst for copolymerizing epoxides and polyols. While excellent utility as a structural adhesive for bonding oily galvanized steel is shown, this particular catalyst system sacrifices pot-life to achieve rapid cure at low to moderate temperatures. U.S. Patent No. 4,751,138 teaches a coated abrasive article prepared by polymerizing a combination of epoxy and acrylate monomers using a combination of photoinitiators which can be cationic organometallic salts, onium salts, or thermally active Lewis acids such as antimony pentafluoride. Stabilization of the Lewis acids by the addition of amines is taught. Australian Patent Application 38551/85 describes a hardenable composition consisting of a) a material polymerizable by cationic or free radical polymerization b) an iron (II)-η 6 -benzene-η 5 -cyclopentadienyl complex salt, c) a sensitizer, and with certain monomers d) an electron acceptor. The electron acceptors are preferably an organic hydroperoxide, an organic peracid or a quinone. U.S. Patent No. 5,073,476 teaches the combination of iron(II) aromatic complexes mixed with electron acceptors for the polymerization by irradiation of organic materials which can be polymerized cationically and/or by free radicals. Nonspecific reference is made to methods to increase the capacity of the compositions to be stored in the dark by the addition of weak organic bases which are broadly stated to be nitriles, amides, lactones or urea derivatives. U.S. Patent No. 5,089,536 disclose curable compositions comprising an ionic salt of an organometallic complex cation and a cationically curable monomer. Novel compounds disclosed therein are claimed in U.S. Patent No. 5,191,101. There is no teaching as to how to increase the shelf life or pot-life of a cationically curable composition. Canadian Patent Application 2,040,010 relates to epoxy resin compositions comprising iron-arene complexes and specific primary amines or bipyridines as inhibitors. The epoxy containing compositions require light activation to cure. U.S. Patent No. 4,503,211 teaches that a latently curable epoxy resin composition including a novel curing agent comprising the liquid salt of a substituted pentafluoroantimonic acid and an aromatic amine has long pot life yet cures rapidly when heated. U.S. Patent No. 5,047,376 teaches the activation of organic cationically polymerizable materials through the use of a dispersion or a solution of an iron/arene salt and a polycarboxylic acid, an anhydride based on a polycarboxylic acid, or a polyisocyanate, by heating or with actinic irradiation. They teach increased shelf life using these compositions. A conductive metal-containing adhesive is disclosed in Canadian Patent No. 1,277,070. Organic solvents useful to make coatable compositions are disclosed and include certain sulfoxides, sulfones, carboxylates, and lactones. Briefly, in one aspect, this invention provides an energy polymerizable composition according to claim 1 comprising: (a) at least one cationically curable monomer selected from the group consisting of epoxy monomers and vinyl ether-containing monomers; (b) a two-component initiator comprising: (1) at least one salt of an organometallic complex cation, and (2) at least one stabilizing additive as described below; (c) abrasive particles; and optionally, at least one of an alcohol containing material, an additive to increase the speed of cure, and additional adjuvants. In a further aspect, the invention provides a process for controlling the cure of a composition comprising the steps of: (a) providing the curable composition of the invention as described above, (b) adding sufficient energy to the composition in the form of at least one of heat and light in any combination and order to cure the composition, wherein energy preferably is heat only. In yet a further aspect, this invention provides an article comprising a substrate having on at least one surface thereof a layer of the composition of the invention. The article can be provided by a method comprising the steps: (a) providing a substrate, (b) coating the substrate with an energy polymerizable composition comprising at least one epoxy monomer or vinyl ether monomer, and a two-component initiator system comprising at least one salt of an organometallic complex cation and at least one stabilizing additive, and optionally adjuvants, as described above; preferably the coating is provided by methods such as bar, knife, reverse roll, extrusion die, knurled roll, or spin coatings, or by spraying, brushing, and (c) supplying sufficient energy to the composition in the form of at least one of heat and light in any combination and order to cure the composition, preferably heat only is used. As used in this application: "energy-induced curing" means curing or polymerization by means of heat or electromagnetic radiation (ultraviolet, visible, or electron beam), or electromagnetic radiation in combination with thermal (infrared and heat) means, such that heat and light are used simultaneously, or in any sequence, for example, heat followed by light, light followed by heat followed by light; preferably thermal energy only is used; "catalytically-effective amount" means a quantity sufficient to effect polymerization of the curable composition to a polymerized product at least to a degree to cause an increase in viscosity of the composition under the conditions specified; "organometallic salt" means an ionic salt of an organometallic complex cation, wherein the cation contains at least one carbon atom of an organic group that is bonded to a metal atom of the transition metal series of the Periodic Table of Elements ("Basic Inorganic Chemistry", F.A. cotton, G. Wilkinson, Wiley, 1976, p 497); "initiator" and "catalyst" are used interchangeably and mean a substance that changes the speed of a chemical reaction; "cationically curable monomer" means at least one epoxide and/or at least one vinyl ether containing material; "polymerizable composition" as used herein means a mixture, of the initiator system and the cationically curable monomer; alcohols, speed enhancers, and adjuvants optionally can be present; "polymerize or cure" means to supply sufficient energy to a composition in the form of at least one of heat and light in any order or combination to alter the physical state of the composition, to make it transform from a fluid to less fluid state, to go from a tacky to a non-tacky state, to go from a soluble to insoluble state, or to decrease the amount of cationically polymerizable material by its consumption in a reaction; "initiation system", "initiator system", or "two-component initiator" means at least one salt of an organometallic complex cation and at least one stabilizing additive, the system being capable of initiating cationic polymerization; "stabilizing additive" means at least one of specified compounds that moderate the cure of a composition of the invention; "group" or "compound" or "ligand" means a chemical species that allows for substitution or which may be substituted by conventional substituents which do not interfere with the desired product, e.g., substituents can be alkyl, alkoxy, aryl, phenyl, halo (F, Cl, Br, I), cyano, nitro, etc., and "epoxy/polyol" and "catalyst/additive", etc., mean combinations of the substances on both sides of the slash ("/"). Applicants have recognized that the industry can benefit from a thermally-curable epoxy or vinyl ether-containing resin composition which has an extended pot life, preferably does not have to be activated by lights yet will cure rapidly over a bread temperature range (50°-200°C) and will retain the desired physical properties as required by its intended use. Applicants believe there is no teaching in the art to polymerization of epoxy or vinyl ether monomers using as initiator system a combination of cationic organometallic salts combined with the class of stabilizers disclosed herein. The present invention provides an energy polymerizable composition comprising at least one epexy monomer or at least one vinyl ether monomer and an initiation system therefor, the initiation system comprising at least one organometallic complex salt and at least one stabilizing additive. The cured composition provides useful articles or coated articles. Epoxy compounds that can be cured or polymerized by the processes of this invention, using a catalytically effective amount of an initiator system comprising an organometallic cation salt and a stabilizing additive, are those known to undergo cationic polymerization and include 1,2-, 1,3-, and 1,4-cyclic ethers (also designated as 1,2-, 1,3-, and 1,4-epoxides) and vinyl ethers. See the "Encyclopedia of Polymer Science and Technology", 6 , (1986), 322, for a description of suitable epoxy resins. In particular, cyclic ethers that are useful include the cycloaliphatic epoxies such as cyclohexene oxide and the ERL™ series type of resins available from Union Carbide, New York, NY, also included are the glycidyl ether type epoxy resins such as the Epon™ series type of epoxy resins available from Shell Chemical Co., Houston, TX, or their equivalent from other manufacturers. The preferred epoxy resins include the ERL™ type of resins especially 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, bis- (3,4-epoxycyclohexyl) adipate and 2-(3,4-epoxycylclohexyl-5,5-spiro-3,4-epoxy) cyclohexene-meta-dioxane and the bisphenol A Epon™ type resins including 2,2-bis-[p-(2,3-epoxypropoxy)phenylpropane and chain extended versions of this material. It is also within the scope of this invention to use a blend of more than one epoxy resin. The vinyl ether containing monomers can be methyl vinyl ether, ethyl vinyl ether, tert-butyl vinyl ether, isobutyl vinyl ether, triethylene glycol divinyl ether (Rapicure™ DVE-3, available from GAF, Wayne, NJ), 1,4-cyclohexanedimethanol divinyl ether (Rapicure™ CHVE, GAF), and the VEctomer™ resins from Allied Signal, such as VEctomer 2010, VEctomer 2020, VEctomer 4010, and VEctomer 4020, or their equivalent from other manufacturers. It is within the scope of this invention to use a blend of more than one vinyl ether resin. It is also possible within the scope of this invention to use one or more epoxy resins blended with one or more vinyl ether resins. The different kinds of resins can be present in any proportion. Suitable salts of organometallic complex cations include, but are not limited to, those salts disclosed in U.S. Patent No. 5,089,536, col. 2, line 48, to col. 16, line 10. In the most preferred compositions of the invention, the organometallic complex salt of the initiator system is represented by the following formula: [(L 1 ) y (L 2 ) z M] +q X n wherein M is selected from the group containing Cr, Ni, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh and Ir; L 1 represents the same or different ligands contributing pi-electrons that can be selected from aromatic compounds and heterocyclic aromatic compounds, and capable of contributing six pi-electrons to the valence shell of M; L 2 represents the same or different ligands contributing pi-electrons that can be selected from cyclopentadienyl and indenyl anion groups, and capable of contributing six pi-electrons to the valence shell of M; q is an integer having a value of 1 or 2, the residual charge of the complex cation; X is an anion selected from organic sulfonate anions and halogen-containing complex anions of a metal or metalloid; y and z are integers having a value of zero, one, or two, provided that the sum of y and z is equal to 2; and n is an integer having a value of 1 or 2, the number of complex anions required to neutralize the charge q on the complex cation. Ligands L 1 and L 2 are well known in the art of transition metal organometallic compounds. Ligand L 1 is provided by any monomeric or polymeric compound having an accessible aromatic group regardless of the total molecular weight of the compound. Illustrative of ligand L 1 are substituted and unsubstituted carbocyclic and heterocyclic aromatic ligands having up to 25 rings and up to 100 carbon atoms and up to 10 heteroatoms selected from nitrogen, sulfur, non-peroxidic oxygen, phosphorus, arsenic, selenium, boron, antimony, tellurium, silicon, germanium, and tin, such as, for example, eta 6 -mesitylene, eta 6 -toluene, eta 6 -p-xylene, eta 6 -cumene, eta 6 -hexamethylbenzene, eta 6 -fluorene, and eta 6 -naphthalene. Other suitable aromatic compounds can be found by consulting any of many chemical handbooks. Illustrative of ligand L 2 are ligands derived from the substituted and unsubstituted eta 5 -cyclopentadienyl anion, for example, eta 5 -cyclopentadienyl anion, eta 5 -methylcyclopentadienyl anion, eta 5 -pentamethylcyclopentadienyl anion, eta 5 -trimethyltincyclopentadienyl anion, eta 5 -triphenylsilylcyclopentadienyl anion, and eta 5 -indenyl anion. Each of the ligands L 1 and L 2 can be substituted by groups that do not interfere with the complexing action of the ligand to the metal atom. Ligands L 1 and L 2 independently can be a unit of a polymer. L 1 , for example, can be the phenyl group in polystyrene. L 2 , for example, can be the cyclopentadiene group in poly(vinylcyclopentadiene). It is preferable that 5 to 50% of the aromatic groups present in the polymer be complexed with metallic cations. Suitable anions, X, in formula I, for use as the counterion in the ionic salts of the organometallic complex cation in the coating compositions are those in which X can be represented by the formula DQ r wherein D is a metal from Groups IB to VIIB and VIII or a metal or metalloid from Groups IIIA to VA of the periodic Table of Elements (CAS notation), Q is a halogen atom, hydroxyl group, a phenyl group, or an alkyl group, and r is an integer having a value of 1 to 6. Preferably, the metals are copper, zinc, titanium, vanadium, chromium, manganese, iron, cobalt, or nickel and the metalloids preferably are boron, aluminum, antimony, tin, arsenic, and phosphorus. Preferably, the halogen atom, Q, is chlorine or fluorine. Illustrative of suitable anions are B(phenyl) 4 - , B(phenyl) 3 (alkyl) - , where alkyl can be ethyl, propyl, butyl, hexyl and the like, BF 4 - , PF 6 - , AsF 6 - , SbF 6 - , FeCl 4 - , SnCl 5 - , SbF 5 OH - , AlCl 4 - , AlF 6 - , GaCl 4 - , InF 4 - , TiF 6 - , ZrF 6 - , etc. Additional suitable anions, X, in formula I, of use as the counterion in the ionic salts of the organometallic complex cations include those in which X is an organic sulfonate. Illustrative of suitable sulfonate-containing anions are CH 3 SO 3 - , CF 3 SO 3 - , C 6 H 5 SO 3 - , p-toluenesulfonate, p-chlorobenzenesulfonate and related isomers. Preferably, the anions are BF 4 - , PF 6 - , SbF 6 - , SbF 5 OH - , AsF 6 - , SbCl 6 - , and CF 3 SO 3 - . Organometallic salts are known in the art and can be prepared as disclosed in, for example, EPO Nos. 094,914, 094,915, 126,712, and U.S. Patent Nos. 5,089,536, 5,059,701, 5,191,101. Also, disubstituted ferrocene derivatives can be prepared by the general procedure described in J. Amer. Chem. Soc. , 1978, 100 , 7264. Ferrocene derivatives can be oxidized to prepare the corresponding ferrocenium salts by the procedure described in Inorg. Chem. , 1971, 10 , 1559. The preferred salts of organometallic complex cations useful in the compositions of the invention are derived from formula I where L 1 is chosen from the class of aromatic compounds, preferably based on benzene, and L 2 is chosen from the class of compounds containing a cyclopentadienyl anion group, M is Fe and X is selected from the group consisting of BF 4 - , PF 6 - , AsF 6 - , SbF 6 - , SbF 5 OH - or trifluoromethanesulfonate. The most preferred salts of the organometallic complex cations useful in the invention are included in formula I where only L 1 or only L 2 is present, M is Fe and X is selected from the group named above. The organometallic complex cations can be used as mixtures and isomeric mixtures. In the preferred compositions of the invention, salts of the organometallic complex cation include those disclosed in U.S. Patent No. 5,089,536. Examples of the preferred salts of organometallic complex cations useful in preparing the compositions of the invention include the following: bis-(eta 6 -durene)iron(2+) hexafluoroantimonate bis-(eta 6 -mesitylene)iron(2+) trifluoromethanesulfonate bis-(eta 6 -mesitylene)iron(2+) hexafluoroantimonate bis-(eta 5 -hexamethylbenzene)iron(2+) hexafluoroantimonate bis-(eta 6 -naphthalene)iron(2+) hexafluoroantimonate (eta 6 -naphthalene) (eta 5 -cyclopentadienyl)iron(1+) hexafluoroantimonate (eta 6 -pyrene) (eta 5 -cyclopentadienyl)iron(1+) trifluoromethanesulfonate bis-(eta 5 -methylcyclopentadienyl)iron(1+) hexafluoroantimonate bis-(eta 5 -cyclopentadienyl)iron(1+) trifluoromethanesulfonate bis-(eta 5 -cyclopentadienyl)iron(1+) hexafluoroantimonate. Stabilizing additives of the present invention can be selected from a class of materials represented by compounds of formulae (V) and (VI). The active portions of these materials (see formulae V and VI which can be converted to an active portion by replacement, for example, of a hydrogen atom by a bonding site), can be part of a polymer or included as part of any component in the compositions of the invention. Stabilizing additives are selected from a class represented by formulae V and VI: wherein each R 2 independently can be hydrogen or is a group selected from C 1 to C 10 alkyl groups and groups having 1 to 4 fused or unfused aromatic rings, and the R 2 s together can form a heterocyclic ring having 5 to 7 ring atoms, or two R 2 s together can form at least one ring which is saturated or unsaturated and the ring can be substituted or unsubstituted with alkyl, alkenyl or alkynyl groups containing from 1 to 30 carbon atoms; the carbon atoms can be interrupted with up to 10 individual, non-catenated heteroatoms selected from O, S, and N. Examples of this class of stabilizer include unsubstituted and substituted phenanthroline compounds, the most common substituents being alkyl groups having 1 to 20 carbon atoms, the preferred phenanthroline being 1,10-phenanthroline; oxygen is not required in this stabilization; and a class of tripyridyltriazines, wherein each R 2 has the same definition as in formula V, with the preferred being 2,4,6-tripyridyltriazine. The initiator system is present in a catalytically effective amount. Typically, the initiator system (two components) can be present in the range of 0.01 to 20% by weight, preferably 0.1 to 5% by weight of the total polymerizable composition. For the stabilizing additive, the mole ratio of the organometallic complex salt to the stabilizing additive is generally in the range of 1:10 to 10:1, preferably 1:5 to 5:1. When it is desired to increase the rate of cure of the compositions of the invention, it can be useful to additionally include a cure rate enhancer such as a peroxide group, hydroperoxide (-OOH group), or acid-generating esters. A description of useful peroxides and hydroperoxides can be found in the "Encyclopedia of Chemical Technology", 17 , 1982, 1-90. Many useful peroxides are commercially available such as di-tert-butyl peroxide or cumene hydroperoxide. Acid-generating esters and their preparation are described in U.S. Patent No. 3,907,706. Preferred esters can be prepared by an esterification reaction between oxalic acid and tertiary alkyl alcohols such as t-butanol and 1,1-dimethylpropanol. Typically the cure rate enhancers can be present in the range of 0.01 to 2.0 percent by weight, preferably 0.1 to 5 percent by weight of the total polymerizable composition. When the resin captains an epoxy, it can also be preferred and within the scope of this invention to add mono- or poly-functional alcohols as tougheners to the epoxy curable composition. The alcohol or polyol aids in chain extension and preventing over-crosslinking of the epoxide during curing. Examples of useful polyols are disclosed in U.S. Patent No. 4,503,211. Higher molecular weight polyols include the polyethylene and polypropylene oxide polymers in the molecular weight range of 200 to 20,000 such as the Carbowax™ polyethyleneoxide materials supplied by Union Carbide, caprolactone polyols in the molecular weight range of 200 to 5,000, such as the Tone™ polyol materials supplied by Union Carbide, polytetramethylene ether glycol in the molecular weight range of 200 to 4,000, such as the Terathane™ materials supplied by Dupont (Wilmington, DE), hydroxyl terminated polybutadiene resins such as the Poly bd™ supplied by Elf Atochem, or equivalent materials supplied by other manufacturers. The alcohol functional component can be present as a mixture of materials and can contain mono- and polyhydroxyl containing materials. The alcohol is preferably present in an amount sufficient to provide an epoxy to hydroxy ratio in the composition between about 1:0.1 and 1:1, more preferably between about 1:0.2 and 1:0.8, and most preferably between about 1:0.3 and 1:0.6. A suitable initiation system that includes organometallic complex ionic salts described by formula I, and at least one stabilizing additive contains those combinations that, upon application of sufficient energy generally in the form of heat and/or light will catalyze the polymerization of the compositions of the invention. The level of catalytic activity depends on various factors such as the choice of ligands and counterions in the organometallic salt and the selection of the at least one stabilizing additive. Temperature of polymerization and amount of initiator system used will vary depending on the particular polymerizable composition used and the desired application of the polymerized product. Solvents, preferably organic, can be used to assist in dissolution of the initiator system in the cationically polymerizable monomers, and as a processing aid. It may be advantageous to prepare a concentrated solution of the organometallic complex salt in a small amount solvent to simplify the preparation of the polymerizable composition. Useful solvents are lactones, such as gamma-butyrolactone, ketones such as acetone, methyl ethyl ketone; sulfones, such as tetramethylene sulfone, 3-methylsulfolane; cyclic carbonates such as propylene carbonate; and other solvents such as methylene chloride, nitromethane, glycol sulfite and 1,2-dimethoxyethane (glyme). In some applications, it may be advantageous to adsorb the initiator onto an inert support such as silica, alumina, clays, as described in U.S. Patent No. 4,677,137. Suitable sources of heat to cure the compositions of the invention include induction heating coils, ovens, hot plates, heat guns, IR sources including lasers, microwave sources, etc. Suitable substrates useful to provide articles of the invention include, for example, metals (for example, aluminum, copper, cadmium, zinc, nickel, steel, iron, silver), glass, paper, wood, various thermoplastic or thermoset films (for example, polyethylene terephthalate, plasticized polyvinyl chloride, polypropylene, polyethylene), cloth, ceramics and cellulosics, such as cellulose acetate. Adjuvants may optionally be added to the compositions such as colorants, abrasive granules, stabilizers, light stabilizers, antioxidants, flow agents, bodying agents, flatting agents, inert fillers, binders, blowing agents, fungicides, bactericides, surfactants, plasticizers, rubber tougheners and other additives known to those skilled in the art. They also can be substantially unreactive, such as fillers both inorganic and organic. These adjuvants, if present are added in an amount effective for their intended purpose. Compositions of this invention are useful to provide abrasion-resistant or protective coatings to articles, as molded articles, as adhesives, including hot melt and structural adhesives, and as binders for abrasives. In general, a composition's physical properties, i.e., hardness, stiffness, modulus, elongation, strength, etc., is determined by the choice of the epoxy resin, and if an alcohol containing material is used, the ratio of epoxy to alcohol and the nature of the alcohol. Depending on the particular use, each one of these physical properties of the system will have a particular optimum value. Generally, the cured material from a higher epoxy/alcohol ratio is stiffer than from a lower epoxy/alcohol ratio. Generally, for an epoxy/alcohol composition, a shorter chain polyol yields a cured composition that is stiffer than when using a longer chain polyol. The stiffness of a composition can also be increased by using a shorter chain monofunctional alcohol to replace a polyol. The speed of cure can be controlled by the choice of initiator system, its level, and the particular curable materials. Epoxy/alcohol mixtures generally cure faster than epoxy only compositions. cycloaliphatic epoxies cure more rapidly than glycidyl ether epoxies. Mixtures of these two types of epoxies can be used to adjust the cure rate to a desired level. To prepare a coated abrasive article using the materials of the subject invention, abrasive particles must be added to the curable composition. The general procedure is to select a suitable substrate such as paper, cloth, polyester, etc., coat this substrate with the make coat which consists of the curable composition containing the abrasive particles, and then curing by the application of a source of energy. A size coat, which cures to a harder material than the make coat, is then coated over the make coat and cured. The size coat serves to lock the abrasive particles in place. Molded articles are made by means known to those skilled in the art, as, for example, by reaction injection molding, casting, etc. Objects and advantages of this invention are further illustrated by the following examples, but they should not be construed as limiting the invention, the scope of which is defined by the claims. EXAMPLES In the examples, all parts, ratios, and percents are by weight unless specifically indicated otherwise. All materials used are either known or commercially available unless otherwise indicated or apparent. All examples were prepared in ambient atmosphere (in the presence of usual amounts of oxygen and water vapor) unless indicated otherwise. The general sample preparation procedure was as follows: the desired amount of stabilizing additive was mixed with the epoxy or vinyl ether containing composition; the composition was warmed if necessary to insure complete mixing or the components; the mixture was allowed to cool to room temperature (23°C) before use. Curable mixtures were prepared by measuring out the desired amount of the cationic organometallic catalyst, and, if needed, adding the desired amount of solvent to dissolve the catalyst, then adding the epoxy or vinyl ether containing mixture and mixing thoroughly. TEST METHODS TENSILE TEST SAMPLE PREPARATION Tensile test samples were prepared by using an ASTM 628-87 Type IV die to cut a mold out of 0.91 millimeter (mm) thick silicone rubber mold. A sandwich construction was prepared by first laying down on an aluminum panel a 0.025 micrometer (µm) polyester sheet coated with a conventional silicone release layer, release side up. The silicone rubber mold was placed on this layer. The polymerizable composition to be cured was applied to the mold. A second piece of release layer coated polyester, release side down, was placed over the mold and a rubber roller was used to smooth out the sample and eliminate air bubbles. The samples were cured with various temperature cycles as stated in the particular example. Using this procedure, reproducible samples were made for tensile tests. TENSILE TESTING PROCEDURE Tensile tests were conducted following the method described in ASTM 628-87 Tensile Testing Methods standard. The samples were tested at a strain rate of 5 mm/min. An Instron Model 1122 tensile tester was used for the tests. Ultimate tensile strength is reported in MPa and is the strength at break, percent elongation is reported in % using the crosshead movement as a measure of elongation, energy at break is reported in Newton-meters (N-m) and is the area under the stress-strain curve and modulus is reported in MPa and is the modulus at 3% elongation. OVERLAP SHEAR TEST Sheets of 0.76 mm thick G60 hot-dipped extra smooth galvanized steel, obtained from National Steel Corporation, Livonia, MI, were cut into 25.4 mm by 76.2 mm test coupons and degreased with acetone. Both coupons are allowed to dry for 30 minutes at about 22°C. The adhesive composition was spread over one end of the first coupon. The spacing distance, 0.254 mm, was maintained by the presence of glass microbeads in the adhesive mix. The other coupon was placed over the adhesive such that there was a 12.7 mm overlap of the coupons and with the uncoated ends of the coupons aligned in opposite directions from each other. The coupons were clamped together and cured at 170°C for 30 minutes. The prepared samples were cooled for at least 1 hour at about 22°C before testing. That lap shear was determined using a tensile tester according to ASTM Test Method D1002-72 with a crosshead speed of 5 cm/min. The lap shear strength was reported in megaPascals (MPa). Differential Scanning Calorimetry (DSC) Differential Scanning Calorimetry was used to measure the exothermie heat of reaction associated with the cure of the cationically polymerizable monomer. This energy is measured in Joule/gram (J/g). The exotherm profile, i.e. peak temperature, onset temperature, etc., of the exotherm provided information on conditions that are needed to cure the material. The integrated energy under an exothermic peak is related to the extent of cure. For a stable composition, more of that exotherm energy should remain with time indicating that the composition is not curing prematurely. For an unstable composition, the exotherm energy will decrease more rapidly with time indicating that the composition has undergone some degree of cure prematurely. GLOSSARY IDENTIFICATION OF COMPONENTS USED IN THE EXAMPLES ERL™-4221 3,4-epoxycyclohexylmethyl-3,4-epoxy cyclohexanecarboxylate (ERL-4221 available from Union Carbide) Epon™ 828 diglycidyl ether of bisphenol A (EPON 828 available from Shell Chemical Co.) CHDM 1,4-cyclohexanedimethanol Paraloid™ BTA IIIN2 brand copolymer methyl methacrylate/butadiene/ styrene copolymer available from Rohm & Haas Company Reactive Diluent WC68™ diglycidyl ether of neopentyl glycol having an epoxy equivalent weight of about 135 available from Rhone-Poulenc GP7I™ silica silicon dioxide having a particle size range from 20-30 micrometers available from Haribson Walker Corp. Cab-O-Sil™ TS720™ brand silica fumed silica available from Cabot Corp. B37/2000™ glass bubbles, available from Minnesota Mining and Manufacturing Company catalysts Cp 2 FeSbF 6 bis-(η 5 -cyclopentadienyl)iron (+1) hexafluoroantimonate (MeCp) 2 FeSbF 6 bis-(η 5 -methylcyclopentadienyl)-iron(+1) hexafluoroantimonate (Me 3 SiCp) 2 FeSbF 6 bis-(η 5 -trimethylsilylcyclopentadienyl)-iron(+1)hexafluoroantimonate (Ph 3 SnCp) 2 FeSbF 6 bis-(η 5 -triphenyltincyclopentadienyl)iron(+1) hexafluoroantimonate CpFeXylSbF 6 (η 6 -xylenes)(η 5 -cyclopentadienyl)iron(+1) hexafluoroantimonate Cp cyclopentadienyl Me methyl Ph phenyl Mes mesitylene Comparative Example C1 To determine the gel time for an unstabilized epoxy composition, 0.01g of Cp 2 FeSbF 6 was weighed into an aluminum dish and 0.025g of gamma-butyrolactone added to completely dissolve the catalyst. To this was added 2.00g of ERL-4221, mixed thoroughly and then placed on a hot plate at 50°C and the time to produce a gel was recorded. The presence of gel was indicated by the formation of insoluble material, or an increase in viscosity. In this example gel was formed after 90 sec at 50°C. Comparative Example C2 To determine the gel time for an unstabilized epoxy composition, 0.01g of Cp 2 FeSbF 6 , was weighed into an aluminum dish and 0.025g of gamma-butyrolactone added, then 2.00g of Epon 828 was added, mixed thoroughly and then placed on a hot plate at 100°C and the time to produce a gel was recorded. The presence of gel was indicated by the presence of insoluble material. Gel was formed after 15 minutes at 100°C. Comparative Examples C3-C6 To test the effect of catalyst concentration on gel time, a series of catalyst/epoxy/polyol compositions were prepared and evaluated following the procedure described in Comparative Example C2. The ratio of epoxy functionality to hydroxyl functionality was selected as 1/0.4. The amount of materials to mix to obtain this ratio was determined by using an epoxy equivalent weight of 188 for the epoxy, Epon 828, and a hydroxyl equivalent weight of 45.06 for the polyol, 1,4-butanediol. The results of these evaluations are shown in Table 1. Compared to the results in Comparative Example C2. The gel times with a polyol present are in general shorter than without the polyol. This makes these compositions more difficult to stabilize. Effect of Catalyst Concentration on Gel Time (min) Comparative Example Catalyst Concentration 100°C 150°C C3 2.0% 1.5 g -- C4 1.0% 5 g -- C5 0.5% 7 g -- C6 0.25% 20 g -- g means gel formed after the specified time Comparative Example C7 (Mesitylene) 2 Fe(SbF 6 ) 2 (0.01 g) was added to an aluminum dish and 0.03 g of gamma-butyrolactone was added to completely dissolve the catalyst. One g of Epon 828 was added and mixed in thoroughly. Several DSC sample pans were prepared, hermetically sealed, and stored at room temperature. Shelf life analysis of the mixture was performed by DSC on the day of preparation (0 weeks), and over time. The data of Table 2 illustrate that the composition used had poor shelf-life with only 26% of the maximum cure energy retained. This means that 74% of the monomer has polymerized. Polymerization Exotherm Profile over Time Reaction Time (weeks) Exotherm Energy (Joules/gram) (°C) (°C) (°C) 0 518 45 98 167 1 278 55 103 120 2 184 >50 106 122 3 167 >50 109 129 4 175 >50 111 124 6 137 >60 111 123 Comparative Example C8 Trials were run to examine the effect of 2-2'-bipyridyl on the shelf-life of epoxy resins. A stock solution of epoxide/additive was prepared by adding 0.10g of finely dispersed bipyridyl to 100g of Epon 828. This mixture was heated to 80°C for approximately 20 minutes with vigorous shaking to ensure complete dissolution of the additive in the epoxide. (Mesitylene) 2 Fe(SbF 6 ) 2 (0.01g) was added to an aluminum dish and 0.04g of 3-methylsulfolane was added to completely dissolve the catalyst. Two g of the stock solution was added and mixed in thoroughly. Several DSC sample pans were prepared and analyzed as in Example C7. The data in Table 3 illustrate that after a six-week period at room temperature, 59% of the maximum exotherm energy was retained, and little change was observed upon longer aging. Polymerization Exotherm Profile over Time Reaction Time (weeks) Exotherm Energy (Joules/gram) T max (°C) 0 452 116 1 495 116 2 468 115 3 493 112 5 424 115 6 290 113 13 312 122 Examples 1 and 2 (not within the claims) Trials were run to examine the effect of 1,10-phenanthroline on the shelf-life of epoxy resins. Stock solutions of epoxide/additive were prepared by adding the appropriate amount (0.12g for Example 1; 0.06 g for Example 2) of finely dispersed 1,10-phenanthroline to 100g of Epon 828. The mixtures were heated to 80°C for approximately 20 minutes with vigorous shaking to ensure complete dissolution of the additive in the epoxide. (Mesitylene) 2 Fe(SbF 6 ) 2 (0.01 g) was added to an aluminum dish and 0.04 g of 3-methylsulfolane was added to completely dissolve the catalyst. Two g of the stock solution was added and mixed in thoroughly. Several DSC sample pans were prepared and analyzed as in Example C7. The data of Table 4 illustrate the stabilizing effect the addition of 1,10-phenanthroline had on the room temperature cure of the composition. The data in Table 4 for Example 1 show that for this formulation 95% of the maximum cure energy was retained after a six-week period at room temperature. Additionally, when compared to the data in Table 3 it can be seen that the formulation containing 1,10-phenanthroline had a longer shelf life than did the formulation containing 2,2'-bipyridyl as was shown in Example C8. Polymerization Exotherm Profile over Time Reaction Time (weeks) Exotherm Energy (Joules/gram) T max (°C) Ex. 1 Ex. 2 Ex. 1 Ex. 2 0 501 500 116 115 1 495 499 118 115 2 454 499 118 115 3 506 512 116 113 4 486 488 116 115 5 504 487 115 113 6 481 427 115 114 Preparation of Adhesive Premix: The epoxy based composition was prepared by combining 59.40 parts Epon 828, 5.87 parts WC68™, 8.88 parts Paraloid BTA IIIN2 copolymer. The mixture was stirred with a high shear mixer at about 115°C for two hours, then cooled to room temperature. To this cooled mixture was added 20.59 parts GP-7I, 1.38 parts B37/2000, 2.58 parts TS-720, and 1.30 parts 0.254 mm (0.01 inch) glass beads (Cataphote, Inc., Jackson, MS) to make 100 parts of composition. High shear mixing was continued for 30 minutes at room temperature (23°C), followed by vacuum degassing at room temperature. This mixture constituted the adhesive premix used in Examples C15-C16 and Examples 35-40. Comparative Examples C9-C13 and Example 3 (not within the claims) Evaluations were performed to determine the initial overlap shear strength of an adhesive formulation, and to monitor the strength over time. Table 5 shows the composition formulations. The adhesive compositions were prepared by dissolution of the cationic organometallic salt and any additional additives in a solvent, followed by addition of the premix and difunctional alcohols. The mixture was stirred until a uniform mixture was obtained. The overlap shear data are shown below in Table 6. Overlap Shear Strength (MPa) over Time Ex. Initial 1 Week 3 Weeks 4 Weeks 6 Weeks C9 10.33 10.55 3 11.75 14.87 11.62 14.24 C11 16.10 16.67 13.83 16.58 15.36 C10 13.51 C12 16.21 15.05 C13 13.90 13.00 Comparative Example C14 A stock solution of 1,10-phenanthroline and epoxy was prepared by mixing 0.12 g of 1,10-phenanthroline with 100 g of an Epon 828/1,6-hexanediol/CHDM (78:11:11 w/w) mixture and mixed in thoroughly. In an aluminum dish, 0.06 g of SbF 5 ·DEG was added to 2.01 g of the stock solution and mixed in thoroughly at room temperature. Gel particles formed upon mixing and a rapid exotherm occurred within 2 minutes. The data of Example 2 show that an analogous resin mixture containing (mesitylene) 2 Fe(SbF 6 ) 2 was stable at room temperature for at least five weeks before slow cure started. The data of Comparative Example C14 show that conventional Lewis acid catalysts must be used in higher concentrations than the organometallic salts disclosed in this invention. Additionally, epoxy mixtures containing this conventional Lewis acid catalyst were not stabilized by the additives in this invention under equivalent conditions used for the cationic organometallic salts. Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope of this invention, and it should be understood that this invention is not to be unduly limited to the illustrative embodiments set forth herein.

Claims: An energy polymerizable composition comprising a) at least one cationically curable monomer selected from the group consisting of epoxy monomers and vinyl ether-containing monomers, b) a two-component initiator comprising (1) at least one salt of an organometallic complex cation comprising at least one carbon atom of an organic group bonded to a transition metal atom, and (2) at least one stabilizing additive, or an active portion thereof, selected from the group which is represented by compounds having the formula (V) wherein each R 2 independently can be hydrogen or is a group selected from C 1 to C 10 alkyl groups and groups having 1 to 4 fused or unfused aromatic rings, and the R 2 s together can form a heterocyclic ring having 5 to 7 ring atoms, or two R 2 s together can form at least one ring which is saturated or unsaturated and the ring can be substituted or unsubstituted with alkyl, alkenyl or alkynyl groups containing from 1 to 30 carbon atoms; the carbon atoms can be interrupted with up to 10 individual, non-catenated heteroatoms selected from O, S, and N; and a class of tripyridyltriazines of the formula (VI) wherein each R 2 independently is as previously defined, and c) abrasive particles; said composition optionally further comprising at least one mono- or poly-alcohol or at least one additive to increase the speed of cure. The composition according to claim 1 wherein said salt of an organemetallic complex cation has the formula [(L 1 ) y (L 2 ) z M] +q X n wherein M is selected from the group containing Cr, Ni, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh and Ir; L 1 represents none, one or two of the same or different ligands contributing pi-electrons that can be selected from aromatic compounds and heterocyclic aromatic compounds, and capable of contributing six pi-electrons to the valence shell of M; L 2 represents none, one or two of the same or different ligands contributing pi-electrons that can be selected from cyclopentadienyl and indenyl anion groups, and capable of contributing six pi-electrons to the valence shell of M; q is an integer having a value of 1 or 2 , the residual charge of the complex cation; y and z are integers having a value of zero, one, or two, provided that the sum of y and z is equal to 2; X is an anion selected from organic sulfonate anions and halogen-containing complex anions of a metal or metalloid; and n is an integer having a value of 1 or 2, the number of complex anions required to neutralize the charge q on the complex cation. The composition according to claims 1 or 2 wherein said salt is selected from the group consisting of bis(eta 6 -arene)iron complex cations and bis(eta 5 -cyclopentadienyl)iron complex cations. The composition according to claim 3 wherein said stabilizing additive is used with bis-(eta 6 -arene)iron complex cations. The cured composition according to any of claims 1 to 4. A process comprising the steps: a) providing the curable composition according to any of claims 1 to 4, and b) adding sufficient energy to the composition in the form of at least one of heat and light in any combination and order to cure said composition. An article comprising a substrate having on at least one surface thereof a layer of the composition according to any of claims 1 to 5. The article according to claim 7 wherein said composition is an adhesive, a protective coating, or a binder for an abrasive coating or a magnetic medium. A process comprising the steps: a) coating at least one surface of a substrate with a layer of the energy polymerizable composition according to any of claims 1 to 4, and b) supplying sufficient energy to the composition in the form of at least one of heat and light in any combination and order for a time sufficient to cure said composition.

Inventors: MAHONEY WAYNE S, PALAZZOTTO MICHAEL C, MAHONEY, WAYNE S., PALAZZOTTO, MICHAEL C.
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1994
Main classification: C08G59
IPC codes: G03F7, C08G65, C08G59